如何将 Android Open Accessory 模式实现为服务? [英] How to implement Android Open Accessory mode as a service?

问题描述

我一直在尝试使用 Android 开放附件开发套件.按照 Google 提供的 DemoKit 示例，我没有遇到任何问题使解决方案适应我的应用程序.我可以很好地检测、通信和分离附件.

I've been playing around with the Android Open Accessory Development Kit. By following the DemoKit example provided by Google, I've had no trouble in adapting the solution to my application. I can detect, communicate, and detach the accessory just fine.

但是，我需要将整个事情作为服务运行.我有一个由 USB_ACCESSORY_ATTACHED 意图启动的基本活动(即，当附件连接时)，并且工作正常.但是，一旦我启动我的服务并在其中运行与常规活动中的工作解决方案相同的代码，我就会收到 IOException(没有这样的设备")每当我尝试与配件通信(监控 arduino 端显示 USB 连接成功).即使我在服务中指定了正确的 BroadcastReceiver，在 onStartCommand 回调方法中注册它，并使用 openAccessory() 设置通信端点，也会发生这种情况.相关代码如下.

However, I would need to run the whole thing as a service. I have a base activity which is launched by the USB_ACCESSORY_ATTACHED intent (that is, when the accessory is connected), and that works fine. But as soon as I start my service and run identical code in it compared to my working solution within a regular activity, I'm receiving an IOException ("no such device") whenever I'm trying to communicate with the accessory (monitoring arduino side shows a successful USB connection). This happens even though I've specified the correct BroadcastReceiver within the service, registered it in the onStartCommand callback method, and set up the communication endpoints with openAccessory(). Relevant code is as follows.

@Override
public void onCreate() {
    Log.d(TAG, "ONCREATE");

    manager = UsbManager.getInstance(this);
    mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(
            ACTION_USB_PERMISSION), 0);

    // Register broadcastreceiver for filtering accessory events
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    filter.addAction(UsbManager.ACTION_USB_ACCESSORY_DETACHED);
    registerReceiver(mUsbReceiver,filter);
    super.onCreate();
}

public int onStartCommand(Intent intent, int flags, int startId) {
    Log.d(TAG, "ONSTARTCOMMAND METHOD ACCESSED");

    if (mInputStream != null && mOutputStream != null) {
        return START_NOT_STICKY;
    }

    UsbAccessory[] accessories = manager.getAccessoryList();
    mAccessory = (accessories == null ? null : accessories[0]);

    if (mAccessory != null) {
        if (manager.hasPermission(mAccessory)) {
            openAccessory();
        } else {
            synchronized (mUsbReceiver) {
                if (!mPermissionRequestPending) {
                    manager.requestPermission(mAccessory,
                            mPermissionIntent);
                    mPermissionRequestPending = true;
                }
            }
        }
    } else {
        Log.d(TAG, "mAccessory is null");
    }
    return START_NOT_STICKY;
}

openAccessory 方法:

openAccessory method:

/**
 * Open the accessory
 */
private void openAccessory() {
    Log.d(TAG, "openAccessory: "+mAccessory);
    mFileDescriptor = manager.openAccessory(mAccessory);
    if (mFileDescriptor != null) {
        FileDescriptor fd = mFileDescriptor.getFileDescriptor();
        mInputStream = new FileInputStream(fd);
        mOutputStream = new FileOutputStream(fd);
        Thread thread = new Thread(null,this,"AccessoryThread");
        thread.start();
    }
}

对可能的解决方案有什么想法吗?

Any ideas for a possible solution?

推荐答案

解决方案很简单.

if (intent.getAction().equals(USB_ACCESSORY_ATTACHED)) {
    Intent i = new Intent(this, YourServiceName.class);
    i.putExtras(intent);
    startService(i);
}

基本上，复制您在启动用于启动服务的 Activity 时收到的 Intent，因为 Intent 包含 ADK 实现所需的附件的详细信息.

Basically, copy the intent that you received when starting your activity that you use to launch the service, because the intent contains the details of the accessory that the ADK implementation needs.

然后，在服务中继续像以前一样实现 ADK 的其余部分.

Then, in the service proceed to implement the rest of ADK exactly as before.

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